The present invention relates to a holding device for inductive heating of billets of metal alloys having thixotropic properties, and for holding and transporting the billets until casting, The invention also relates to the use of the holding device.
Known are e.g. billets or preforms of metal alloys that are manufactured by melting and continuously casting a metal alloy. The melted alloy is processed e.g. by strong stirring at controlled temperature to a semi-solid alloy state in which the partially melted dendritic primary, solid particles are surrounded by a matrix of liquid metal. This semi-solid alloy mix is cast into elongated ingots, under the influence of stirring, and cooled. The ingots may be processed further in this form, worked into preforms or divided into billets. Processing the ingots, preforms or, in particular, billets may take place for example by e.g. heating a billet such that it reaches a semi-solid, in particular thixotropic, state and then working the billet into a shaped form. This shaping process may be in the form of extrusion, forging or casting. Technologies of this kind are known e.g. from the German patent document DE-PS 22 29 453; technical refinements to this are recorded e.g. in DE-PS 30 06 618. The patent document EP 0 131 175 describes a process for continuous production of metal shapes. To manufacture metal shapes, free-standing metal preforms are heated until reaching a semisolid state i.e. the preforms stand free and the temperature is maintained at a level at which the preform is partially solid. The preforms are transferred by a carrying facility to the shaping facility, said transfer taking place without any significant deformation of the preform and without any significant variation in the semi-solid fraction within the preform. The transfer takes place in particular by means of mechanical gripping. Described in EP A 0 513 523 is another casting process in which the metallic melt is brought into a semi-solid state by means of a static mixer and cooled. The billets produced in this manner are heated e.g. in a stainless steel container and fed into the casting chamber of a casting machine.
During the heating up stage it is decisive that various requirements are satisfied in order for the best quality of billet and end product to be achieved. This concerns e.g. uniformity with respect to maintaining the shape of the semi-solid billet and a uniform distribution of temperature in the billet. Also desired is low metal loss e.g. due to metal dripping off the billet, rapid heating up, in order that no grain growth takes place and an exact and reproducible condition at temperature.